A. Field of the Invention
The present invention relates to a moisture impervious panel, and more particularly, to a moisture impervious panel particularly suitable as a water barrier for a roofing surface, having a central, rigid support structure filled above and below with a mixture of water-swellable bentonite clay and a compressible filler.
One problem in the existing roof structures wherein roofing sheets form an outer barrier is that water often penetrates the outside barrier and migrates along the junction between the roof and the undersurface of the outer barrier until it finds a spot at which it can penetrate the roof and enter the building. It is not unusual to have a leak in the outer barrier and a leak in the building located from 30 to 100 feet apart. In many roofs, the outer roof barrier is a concrete wear surface, such as that in a parking garage. When the expansion joints of such a concrete wear surface open as a result of a drop in temperature, water can easily pass through the wear surface and leak through the roof into the parking garage. The water-impervious panel of the present invention is sandwiched between the roof and the outer roof wear surface to prevent water which has penetrated the outer wear surface from also penetrating the roof.
B. Prior Art
To prevent water which has penetrated an outer wear surface from reaching a roof, sheets of tar paper or other water impervious, flexible sheets have been used to cover the roof and the flexible sheets are covered with a wear surface. The wear surface, such as one inch pad of concrete, is poured over the flexible sheets, thereby holding the sheets in place. It has been found that the constant expansion and shrinkage of the outer wear surface caused by changes in temperatures tears the water impervious flexible sheets thereunder thereby rendering the sheets ineffective.
As one solution to this problem, the water impervious roofing panel disclosed in my prior U.S. Pat. No. 3,466,287 includes a rigid, non-biodegradable upper surface so that expansion and contraction of the upper wear surface cannot tear the water-imperious panel. My prior U.S. Pat. No. 3,466,287 discloses the use of a mixture of finely divided bentonite clay and a compressible filler to form a waterproof barrier for roof constructions. The bentonite is combined with sufficient compressible filler such that the bentonite can expand, when wetted, without buckling the roof. The composition is applied wet to the undersurface of a rigid, durable sheet having embossed dimples to adhere the composition to the undersurface of the dimples. On top of the rigid sheet, a suitable wear surface such as concrete, or a plurality of plys of roofing paper, is applied as an outer barrier. The rigid outer surface of the moisture impervious panel was thought essential because of expansion and contraction of the wear surface and continued traffic on said wear surface which would cause the bentonite composition of a flexible sheet to extrude and render the panel ineffective.